Reduction of graphene oxide to graphene in high boiling point solvents

ABSTRACT

A method of creating graphene comprising the steps of dispersing graphene oxide into water to form a dispersion. Where the method further comprises adding a solvent to the dispersion to form a solution, and controlling a temperature of the solution to form graphene.

TECHNICAL FIELD

This invention relates generally to a method of reducing graphene oxideto graphene and, more particularly, to a method of reducing grapheneoxide to graphene in high boiling point solvents.

BACKGROUND

Graphene is an emerging material with potential use in electronics andmaterial sciences. Researchers are always trying to find easier and moreefficient ways to create graphene. One method of creating grapheneinvolves reducing graphene oxide to graphene. Graphene oxide is alayered material derived from the oxidation of graphite and isdispersible in water as independent sheets. These sheets may be reducedto graphene by deoxygenating the graphene oxide. As the reductionoccurs, it is typical for the graphene sheets to agglomerate with eachother, thus crashing as a solid precipitate. A goal is to maintain theuniform dispersibility of these sheets. In other words, agglomeration orclumping in the final product should be minimized as much as possible.

One chemical method of deoxygenating graphene oxide uses hydrazine.Exposing a graphene oxide solution to hydrazine typically causesgraphene platelets to precipitate out of the solution. Recent literaturereports indicate that careful control of pH and hydrazine concentrationcan alleviate the tendency of the graphene sheets to agglomerate uponreduction. The requirements of carefully adjusted pH and the removal ofhydrazine using dialysis, render this method commercially unattractive.Hydrazine is also a hazardous material that is explosive and highlytoxic. The use of hydrazine in this process means that special handlingis needed. Also, when using hydrazine, platelets of the graphene tend toagglomerate or clump over prolonged periods. A method of producinggraphene without dangerous chemicals would be desirable. A dispersion ofindividual sheets of graphene that does not contain clumps is moredesirable and allows for the use of the resultant product inapplications, such as transparent conductors, filler materials forcomposites or polymeric films.

Thermal deoxygenating is another method of deoxygenating sheets ofgraphene oxide. This method, however, requires exposing the grapheneoxide to temperatures in excess of 1000° C. This process is also slowand requires the use of an inert gas atmosphere, such as Argon. Therequirement for an inert gas atmosphere and exceedingly hightemperatures makes the creation of graphene more cumbersome. The productof thermal decomposition tends to occur as crumpled sheets instead offlat sheets which also limit the commercial usefulness of the sheets.

SUMMARY

One embodiment of a method and composition is a method of creatinggraphene comprising the steps of dispersing graphene oxide into water toform a dispersion. The method further comprises adding a solvent to thedispersion to form a solution, and controlling a temperature of thesolution to form dispersible graphene.

Another embodiment of the method and composition is a compositioncomprising reduced graphitic carbon and a solvent where the solvent isat least one of n-methylpyrrolidone, ethylene glycol, glycerin anddimethylpyrrolidone.

DESCRIPTION OF THE DRAWINGS

The features of the embodiments of the present method and compositionare set forth with particularity in the appended claims. Theseembodiments may best be understood by reference to the followingdescription taken in conjunction with the accompanying drawings, in theseveral figures of which like reference numerals identify like elements,and in which:

FIG. 1 is a flow chart depicting steps comprising a first embodiment ofa method of reducing graphene oxide to graphene.

FIG. 2 is a flow chart depicting steps comprising a second embodiment ofthe method of reducing graphene oxide to graphene.

DETAILED DESCRIPTION

Embodiments of the present method and composition are a description ofreducing graphene oxide to graphene in high boiling point solvents.

As one of ordinary skill in the art will readily appreciate, grapheneoxide decomposes to graphene when heated to temperatures around 200° C.When graphene oxide decomposes to graphene, however, it is desirable tokeep the graphene as a dispersion so that it can be more easily used incommercial products. One way to reduce graphene oxide to graphene is todeoxygenate the graphene oxide.

Graphene oxide typically appears as water dispersible sheets. Thegraphene oxide may be reduced to graphene by deoxygenating the grapheneoxide sheets to obtain sheets of graphene. When reducing the grapheneoxide to graphene, graphene platelets tend to clump up or agglomerate.As mentioned, it is desirable to keep the graphene oxide as a dispersionas the graphene oxide is reduced to graphene.

A method that may lead to the production of dispersible sheets ofgraphene involves dispersing graphene oxide in water to achieve adispersion of single graphene oxide sheets and then adding a highboiling point solvent to the dispersion to form a solution. The highboiling point solvent may be a solvent with a boiling point ofapproximately 200° C. or higher. Because the solvent has a high boilingpoint, the solution may be heated to approximately 200° C. withoutboiling off the solvent while deoxygenating the graphene oxide andultimately to arriving at dispersible graphene. A more detaileddescription of this method follows.

Turning to FIG. 1, which is a flow chart that depicts a first embodiment100 of a method of reducing graphene oxide to graphene. In step 110, adispersion is created. The dispersion may be comprised of graphene oxidedispersed into water by sonication. Sonication as described herein maycomprise inducing cavitation through the use of ultrasound for thepurpose of achieving a dispersion. The graphene oxide may be in the formof water dispersible sheets. Dispersing the graphene oxide by sonicationmay result in a dispersion comprised of single platelets of grapheneoxide. The single platelets of graphene oxide may form a more stabledispersion. A stable dispersion of graphene oxide may be amenable toforming a dispersion of graphene. A ratio of water to graphene oxide inthe dispersion may be approximately one milligram of graphene oxide toapproximately one milliliter of water

A solvent may be added to the dispersion 120 to form a solution. Thesolvent may be a water miscible solvent, such as, for examplen-methylpyrrolidone, ethylene glycol, glycerin, dimethylpyrrolidone,acetone, tetrahydrofuran, acetonitrile, dimethylformamide, an amine oran alcohol. The amount of solvent added to the dispersion may beapproximately equivalent to the amount of the dispersion. Thus if thedispersion is comprised of one milliliter of water and one milligram ofgraphene oxide, a volume or amount of solvent that is approximatelyequivalent to one milliliter of water and one milligram of grapheneoxide may be added to the dispersion. At this point the solution may becomprised of a mixture with a value that is approximately half grapheneoxide/water dispersion and half high boiling point solvent.

The solution may be gradually heated to approximately 200° C. 130. Insome embodiments, the solution may be heated in an autoclave or highpressure chamber. As one of ordinary skill in the art will readilyappreciate, heating the solution in a pressurized environment may raisethe boiling point of the solution, including the solvent. Thus, theboiling point of the solution may reach or exceed 200° C. If thesolution is heated in a pressurized environment, a solvent with aboiling point that is slightly below 200° C. may be used.

As the solution is heated the solution may be stirred. Water may beremoved via evaporation from the solution as the solution is heated. Aswater is removed, the temperature of the solution is expected to rise.As the temperature rises the graphene oxide deoxygenates. When thetemperature of the solution reaches approximately 200° C. a reductionmay be formed. As the solution is heated, the surface of the grapheneoxide may be functionalized, which may result in less clumping of theplatelets in the final product. In an embodiment, the temperature may beheld at approximately 200° C. for a period of time 140 to aid infunctionalization of the reduction. In some embodiments the temperaturemay be held for as little as one hour. In other embodiments thetemperature may be held as long as twenty-four hours. In still otherembodiments the solution temperature may be held only a moment once thetemperature reaches approximately 200° C. to form a reduction.

The reduction may be removed from the heat to allow cooling. Because thereduction may still comprise solvent, the reduction may be purified toremove as much of the remaining solvent as possible 150. Purifying thereduction may comprise filtrating the reduction. The reduction may alsobe re-disbursed in acetone and may be centrifuged as part of thepurification process. The end result of the purification process may bea solid. The solid may be graphene comprising trace amounts of thesolvent.

Turning to FIG. 2, which is a flow-chart that depicts a secondembodiment 200 of the method of reducing graphene oxide to graphene. Instep 210 of the method a dispersion is created. The dispersion may becomprised of water dispersible sheets of graphene oxide dispersed intowater by sonication. The ratio of water to graphene oxide may beapproximately two milligrams of graphene oxide to approximately onemilligram of water.

A solvent may be added to the dispersion 220 to form a solution. Thesolvent may be a water miscible solvent, such as, for examplen-methlypyrrolidone, ethylene glycol, glycerin, dimethlypyrrolidone,acetone, tetrahydrofuran, acetonitrile, dimethylformamide, an amine oran alcohol. The amount of solvent added to the dispersion may beapproximately equivalent to one half the amount of the dispersion. Theif the dispersion is comprised of approximately two milligrams ofgraphene oxide and approximately one milligram of water, the amount ofsolvent added to the dispersion may be approximately one half the volumeor amount of approximately two milligrams of graphene and approximatelyone milligram of water.

The solution may be gradually heated 230. In some embodiments, thesolution may be heated in an autoclave or high pressure chamber. As oneof ordinary skill in the art will readily appreciate, heating thesolution in a pressurized environment may raise the boiling point of thesolution, including the solvent. Thus, the boiling point of the solutionmay reach or exceed 200° C. If the solution is heated in a pressurizedenvironment, a solvent with a boiling point that is slightly below 200°C. may be used.

As the solution is heated the solution may be stirred. As the solutionis heated and stirred water may evaporate from the solution. As waterevaporates from the solution, an amount of solvent approximatelyequivalent to an amount of evaporated water may be added to thedispersion. The steps of gradually heating the solution, stirring thesolution and adding solvent to replace evaporated water may continueuntil the temperature of the solution reaches approximately 200° C. Whenthe temperature reaches approximately 200° C. a reduction may be formed.As the solution is heated, the surface of the graphene oxide may befunctionalized, which may result in less clumping of the platelets inthe final product. In an embodiment, the temperature may be held at 200°C. for a period of time 240 to aid in functionalization of thereduction. In some embodiments the temperature may be held for as littleas one hour. In other embodiments the temperature may be held as long astwenty-four hours. In still other embodiments the temperature may beheld only a moment once the temperature of the solution reachesapproximately 200° C. to form a reduction.

The reduction may be removed from the heat to allow cooling. The cooledreduction may be purified 260. Purifying the reduction may comprisefiltrating the reduction in an effort to remove solvent remaining in thereduction. The reduction may be re-disbursed in acetone and may becentrifuged to recover a solid. The solid may be graphene comprisingtrace amounts of the solvent.

The present method and composition are not limited to the particulardetails of the depicted embodiments and other modifications andapplications are contemplated. Certain other changes may be made in theabove-described embodiments without departing from the true spirit andscope of the present method and composition herein involved. It isintended, therefore, that the subject matter in the above depictionshall be interpreted as illustrative and not in a limiting sense.

1. A method of creating graphene comprising the steps of: dispersinggraphene oxide into water to form a dispersion; adding a solvent to thedispersion to form a solution; and controlling a temperature of thesolution to form graphene.
 2. The method of claim 1 wherein dispersingthe graphene oxide into water further comprises dispersing the grapheneoxide into the water by sonication.
 3. The method of claim 1 wherein thedispersion comprises a ratio of approximately one milligram of grapheneoxide to approximately one milliliter of water.
 4. The method of claim 1wherein the solvent is a water miscible solvent.
 5. The method of claim4 wherein the water miscible solvent is at least one ofn-methylpyrrolidone, ethylene glycol, glycerin, dimethylpyrrolidone,acetone, tetrahydrofuran, acetonitrile, dimethylformamide, an amine andan alcohol.
 6. The method of claim 1 wherein adding solvent to thedispersion further comprises adding an amount of solvent approximatelyequivalent to the amount of the dispersion.
 7. The method of claim 1wherein controlling the temperature of the solution further comprisesheating the solution to approximately 200° C. to form a reduction. 8.The method of claim 7 further comprising the step of stirring thesolution while heating the solution.
 9. The method of claim 7 furthercomprising the step of holding a temperature of the solution atapproximately 200° C.
 10. The method of claim 7 further comprisingholding a temperature of the solution once the water has evaporated fromthe solution.
 11. The method of claim 7 further comprising heating thesolution in at least one of an autoclave and a high pressure chamber.12. The method of claim 7 further comprising purifying the reduction.13. The method of claim 12 wherein purifying the reduction furthercomprises the steps of: dispersing the reduction in acetone to form adispersed reduction; centrifuging the dispersed reduction; and filteringthe dispersed reduction in acetone.
 14. The method of claim 1 whereinthe graphene oxide is dispersed in water by sonication, and thedispersion comprises a ratio of approximately two milligrams of grapheneoxide to approximately one milliliter of water.
 15. The method of claim14 wherein the solvent is a water miscible solvent that is at least oneof n-methylpyrrolidone, ethylene glycol, glycerin, dimethylpyrrolidone,acetone, tetrahydrofuran, acetonitrile, dimethylformamide, an amine andan alcohol.
 16. The method of claim 14 wherein adding solvent to thedispersion further comprises adding an amount of solvent approximatelyequivalent to one half the amount of dispersion.
 17. The method of claim14 wherein controlling the temperature of the solution further comprisesthe steps of: heating the solution to approximately 200° C.; adding,intermittently, solvent to the solution as water boils off such that theamount of solvent added is approximately equivalent to the amount ofwater that has boiled off; stirring the solution; and holding thetemperature of the solution to form a reduction once all the water hasevaporated.
 18. The method of claim 17 wherein controlling thetemperature of the solution further comprises heating the solution in anautoclave or a high pressure chamber.
 19. The method of claim 18 furthercomprising purifying the reduction.
 20. The method of claim 19 whereinpurifying the reduction further comprises the steps of: dispersing thereduction in acetone to form a dispersed reduction; centrifuging thedispersed reduction; and filtering the dispersed reduction in acetone.21. A composition of graphene comprising reduced graphitic carbon and awater miscible solvent wherein the water miscible solvent is at leastone of n-methylpyrrolidone, ethylene glycol, glycerin,dimethylpyrrolidone, acetone, tetrahydrofuran, acetonitrile,dimethylformamide, an amine and an alcohol.